1. Field of the Invention
The invention relates to a robotic arm, and more particularly, to a robotic arm for transporting a substrate in an ultrahigh vacuum capable of performing rotation without any angle limitations and suitable for high pressure equipment and high corrosiveness environment.
2. Description of the Prior Art
With the development of the technology, the size of the electronic device is continuously shrunk, and the circuit becomes more and more complicated, additionally, the requirement and standard for the cleanness in various optoelectronic and semiconductor device manufacturing processes are also increased. In general, there are several indexes to evaluate the technology quality of the electrical device, such as the number of defects, the concentration of impurities, and the flatness of surface. Therefore, in order to increase the yield and production capacity, the automatic manufacturing process equipment must strictly control the amount of particles in the clean room, and the equipment for ultrahigh vacuum (10−7 Torr) or special gas processing should be also strictly controlled.
Please refer to FIG. 1. FIG. 1 shows a scheme diagram of a vacuum interface 22 of a conventional robotic arm. As shown in FIG. 1, the vacuum interface 22 includes ferrofluidic seals 220, an inner shaft 222, an outer shaft 224, an adapter 226, and a bellows 24.
In general, the motion of a substrate transporting arm has three degrees of freedom, such as rotation, extension, and lifting. Conventionally, at least two motors are needed to drive the robotic arm to perform the above-mentioned movements of three degrees of freedom, and at least one motor is set on the rotation component. It is hard for the rotation component to perform a rotation of large angle due to the wiring of the electricity and signal lines, and it is also hard to achieve dynamic balance of the rotation component. Moreover, because the mass of the motor will increase the moment of inertia of the rotation component, when the conventional robotic arm rotates, many drawbacks will be generated, such as poor rigidity, slow transient response, and low rotation speed.
Additionally, since the conventional robotic arm uses the ferrofluidic seals 220 as rotary feedthrough interface, there is a lot of friction within seals and start-up torque is very high due to friction. Besides, the vapor pressure of ferrofluid introduces the risk of molecular contamination and also limits the degree of vacuum. In fact, the ferrofluidic seals need to be periodically maintained, repaired, and replaced. Especially, when the robotic arm is used in a special gas environment, a special ferrofluidic seals is needed, so that the cost of the robotic arm is increased.